Torque control for impact wrenches



Oct. 30, 1956 L". A. AMTsBERG 2,768,546

Y ToRQuE CONTROL FQR IMPACT wRENcHEs Filed April 26, 1954 3 Sheets-Sheer1 mm .m mb .mm 1| mb mw Oct. 30, 1956 L. A. AMTsB-ERG 2,768,546

TORQUE CONTROL FOR IMPACT WRENCHES Filed April 26, 1954 u Y x V J4 MZ 5Sheets-Shee1 2 Tui-7' za INVENTOR ATTORNEY Oct. 30, 1956 L A. AMTsBr-:RG2,768,546

' TORQUE CONTROL FOR IMPACT WRENCHES Filed April 26, 1954 3 Sheets-Sheet3 fg g '//5 www@ ATTORNEY United States Patent() TORQUE CONTROL FORIMPACT WRENCHES Lester A. Amtsberg, Utica, N. Y., assignor to ChicagoPneumatic Tool Company, New York, N. Y., a corporation of New JerseyApplication April 26, 1954, Serial No. 425,689

17 Claims. (Cl. 81-52.3)

This invention relates to impact wrenches and more particularly to adevice for controlling the degree of tightness of a bolt, nut, screw orother object driven by the wrench.

In the use of impact wrenches, for example in the construction ofbuildings and bridges, it is very important to drive the nut to theproper degree of tightness within a short time. This is usuallyaccomplished by a tool having sufcient power and speed to attain thecorrect tightness rather quickly, whereupon the power to the tool mustbe cut-olf immediately to prevent excessive tightness and possibledamage to the threads. In most instances the 'cut-off is effectedmanually and since the tightness varies with the skill of the operator,the driven nut must be tested by a hand torque wrench to determinewhether it is driven properly or is too loose or too tight.

The general object of this invention is the provision of a torquecontrol for an impact wrench which automatically cuts off the power uponattainment of a predetermined tightness ofthe driven bolt. A morespecific object is to obtain uniformity, within close limits, in thetightness of the driven bolt or nut, independently of variations in theair pressure, skill of the operator, the size of the driven bolt, andthe dimensions and structural characteristics of the plates beingbolted.

Another object is to avoid the necessity for testing the bolt after ithas been driven.

A further object is to permit the motor to run at a suiiciently highspeed to complete the impacting cycle quickly without danger of drivingthe bolt too tight.

A still further object is to minimize the work being done by theoperator, by making the operation as automatic as possible.

The design of an automatic cut-off for an impact wrench presents aspecial problem because the instantaneous torque delivered by the hammerto the anvil is not necessarily an accurate indication of the degree oftightness of the driven nut. It often happens that the first blow in aseries of impacts, which occurs under relatively slight resistance torotation but at a relatively high speed of the motor, will beaccompanied by an instantaneous torque of extremely short duration butdisproportionately high value due to the inertia of the anvil uponacceleration thereof. Subsequent impacts are delivered at a slower speedof the hammer, but with greater resistance of the driven nut, ascompared with the rst impact. As the impacting continues the torquedelivered by the hammer to the anvil is greater than during thepreceding impact, until the torque attains a value corresponding to themaximum tightness of the driven nut at which point the power is cut off.

It is accordingly a further object of this invention to provide anautomatic cut-off which operates whenever a hammer blow of nite durationattains a predetermined value of torque, but which is unresponsive to atorsional impulse of infinitesimal duration, such as occurs on thedelivery of the trst blow, even though the instantaneous 2,768,546Patented Oct. 30, 1956 torque be greater than the amount at which thecontrol device responds, to cut-olf the power.

Still another object is the provision of a torque control of simpleconstruction that does not appreciably add to the size or Weight of theimpact wrench.

Another object is a provision of a torque control of durableconstruction having long life and requiring minimum maintenance.

In accordance with this invention the torque control is driven by amotor shaft extending rearwardly or in the opposite direction from theshaft which drives the impact clutch. The rear shaft drives a ball camwhich in turn drives a flywheel during the time that the motor isaccelerating. When the hammer and driving motor are brought to a stop,upon delivery of a rotational impact to the anvil, the ywheel continuesto rotate and delivers torque to the rear motor shaft by way of the ballcam connection. The torque thus delivered is proportional to the torquebeingdelivered to the anvil during the impact blow, because it isproportional to the rate deceleration of the hammer. The axial componentof this force exerted by the cam is likewise proportional. When thisforce exceeds the preload of a spring, the cam moves axially and tripsan automatic control valve to the closed position. The valve remainsclosed until the hand operated throttle valve is closed.

Another object of this invention is to enable the impact wrench to beused for driving left hand as well as right hand bolts, withoutdisturbing the setting of the control device, with the torque release inthe left hand direction being the same as, or proportional to, thetorque release for right hand rotation.

A feature of this invention resides in the use of ball bearings tominimize friction between the parts of the control device, and therebyinsure accuracy. Another feature resides in an adjusting screw,conveniently accessible, for regulating the torque at which the controldevice operates.

Other objects and features will appear more fully from the descriptionwhich follows.

In the accompanying drawings, Figs. 1-18 disclose one I form ofinvention; Figs. 19-25, 28 and 29 show a modification; and Figs. 26 and27 show further modications. Fig. 1 is a longitudinal section of animpact wrench embodying one form of this invention.

Fig. 2 is a cross-section as indicated by the arrows 2 in Fig. l, butwith the impact clutch hammer moved to a diiferent position.

Figs. 3 and 4 are cross-sections as indicated by the arrows 3 and 4respectively in Fig. l.

Fig. 5 is a fragmentary cross-section, in the same plane as Fig. 2,showing the hammer element in a different position.

Fig. 6 is a fragmentary view in longitudinal section similar to Fig. 1but on a larger scale and with the parts in initial running condition.

Fig. 7 is a view similar to Fig. 6 but with the torque control apparatusin the process of operation, and with the automatic control valve movingtoward closed position.

Fig. 8 is a cross-section along the irregular line 8 8 in Fig. l.

Fig. 9 is a fragmentary view, in elevation, of the rear end of the rotorshaft.

Fig. 10 is an end view of the same.

Fig. 11 is alongitudinal section of the ily-wheel or inertia sleeve asindicated by the arrows 11 in Fig. l2.

Fig. 12 is an elevational view of the rear side of the 1ly-wheel.

Fig. 13 is a longitudinal section of the ily-wheel as indicated by thearrows 13 in Fig. 12.

Fig. 14 is a front elevational view of the cam which drives the ywheel.

Fig. 15 is a side elevational view of the cam.

Fig. 16 is a rear elevational view of the cam.

Fig. 17 is a development showing the relation between the cam, ball andfly-wheel when the parts of the tool are in their normal position.

Fig. 18 is a View similar to Fig. 17 but with the ball and cam shiftedto the operated position.

Fig. 19 is a fragmentary view in longitudinal section, of a modifiedtorque control apparatus.

Fig. 20 is a view similar to Fig. 19 but with the trigger operated andthe control valve moving to closed position.

Fig. 21 is a view partly in side elevation and partly in lection of themodied cam forming part of the device of Fig. 22 is a rear view inelevation of the cam shown in Fig. 21.

Fig. 23 is a front view of the modified ily-wheel.

Fig. 24 is a longitudinal section through said fly-wheel.

Fig. 25 is a development of the cam groove or pocket in said flywheel.

Figs. 26 and 27 are developments similar to Fig. 25 but showing modifiedcam grooves.

Fig. 28 is a development of the ball cam connection in the Fig. 19device.

Fig. 29 is a view similar to Fig. 28 but with the parts in the operatedposition.

Fig. 6-16 and 19-24 are drawn to a larger scale than Figs. l-5. Thedevelopment views in Figs. 17, 18 and 25-29 are on a still larger scale.

In the embodiment of invention illustrated in Figs. l- 18, the impactwrench, which is of the pneumatic type, comprises a clutch housing 18, amotor housing 19, and `a control housing 2G, secured in xed relation byany suitable means, such as the usual arrangement of bolts and flanges(not shown). The control housing extends rearwardly to form a griphandle 21. by means of which the tool may be manually held. An auxiliaryhandle (not shown) extends radially from clutch housing 22.

A reversible air motor 23 within the motor housing includes a cylinderor cylinder liner 24, the ends of which abut against end plates 25. Therear end plate has a flange 26 fitting a recess in the control housing20 and a peripheral portion fitting the motor housing 19. The ilange 26surrounds and supports a ball bearing 27.

Abutting the forward side of the front end plate 25 is a ball bearing 28supported within motor housing 19. Ball bearings 27 and 2S `respectivelysupport rear and front shafts 29 and 30 integral with and projectingfrom a rotor 31. As shown in Figs. 1 and 4, the rotor 31 is ofcylindrical shape and is arranged coaxially with its shafts and with theclutch housing 1S, but eccentric with the cylinder 24 to provide acrescent shaped chamber 32 between the rotor and cylinder. The rotor hasa pluraliy of radial slots 33 in which blades 34 are mounted formovement with their outer edges in scraping contact with the cylinder 24to divide the crescent shaped chamber into a series of pockets betweenthe inlet and exhaust ends. A reverse valve 35, operated by a lever 36,controls the direction of ow of the live air and hence the direction of`rotation of the motor 23.

Impact clutch Positioned centrally of the clutch housing is a rotatabletool head 38 having a elongated shank 39 and having an anvil portioncomprising jaws or shoulders 41 adapted to receive rotational impacts ashereinafter described. Under the usual operating conditions, theseimpacts tend to misalign the tool axis. To resist such tendency the toolhead is supported at its forward portion in a steel bushing 42 afiixedto the clutch housing and at its rear end by the rotor shaft 3G whichprojects into a recess 43 formed in the tool head. Also supporting `therear end of the tool head is a clutch driving cam 44 whose front portionsurrounds the recessed end of the tool head and whose rear portion issupported in a ball bearing 4S mounted in the front wall of the motorhousing 19. The driving cam 44 has a splined connection 46 with thefront rotor shaft 30 and rotates in unison therewith. The driving camrotates at times on the tool head 58 but docs not move axially thereon,being confined between the inner race of ball bearing 28 and a shoulder47 on the tool head. Shoulder 47 of course also prevents rearward axialmovement of the tool head. Forward movement of the tool head isprevented by the engagement of the front end of the anvil jaws 41 with asleeve 48 which iits over the shank 38 of the tool head and which abutsagainst a front washer 49 seated against bushing 42. The front end ofthe tool head 38 has a driving connection with a wrench socket 5t)adapted to receive the head of a bolt or other element (not shown) whichis to be driven.

The hammer assembly surrounds the tool head 38 and comprises a cage 51having front and rear plates 52 and 53 integrally connected by anarcuate web 54. The cage is confined against axial movement and at itsopposite ends is arranged to abut against the front washer 49 and a rearwasher 5S which is disposed in front of the inner race of ball bearing45. The hammer cage 51 is arranged for coaxial rotative movementrelative to the tool head 38 and accordingly the front plate 52 is boredto iit the sleeve 48 on the shank 39. rl'he rear plate 53 is bored to tover a cylindrical portion of the driving cam 44 and is permitted tooscillate or turn relative to the cam 44 and motor shaft 3i). Extendingbetween the front and rear plates 52, 53, on the side of the cageopposite the connecting portion 44, is a pin 56. The pin extendsparallel to the axis of the tool head 38 and provides a pivotal supportfor a hammer' element 57. As shown in Figs. l and 3, the hammer elementcomprises a central pivotal portion 57P apertured to t over the pin 56and loosely abutting the front and rear plates 52 and 53 on the hammercage 51. The hammer element 57 also comprises a pair of dogs 57R and 57Lsymmetrically arranged for right and left hand drive respectively andextending forwardly and inwardly from the pivotal portion 57i. At itsfront and inner extremity each dog has a striking surface or impactshoulder 57S engageable with the anvil jaws or shoulders 41 ashereinafter more fully described.

The hammer element 57 is provided with a cam surface 57C which extendsbetween the striking surfaces 57S. The cam surface has the general shapeof a sector of a cylinder whose center lies on the near side of the axisof revolution of the clutch `and extends parallel to said axis.

The impact clutch when driven in a clockwise direction (looking forward)operates in the following manner: The driving cam 44, having a directconnection with the rotor shaft 30, delivers force to the hammer element57, along a line which lies intermediate the axis of revolution of thehammer cage assembly and the individual axis 56 about which the hammerelement 57 may oscillate. The force of the driving cam is resolved intotwo components, one of which imparts a motion of revolution to thehammer element about the axis of tool head, and another of which ends torock the hammer dog 57K out of driving engagement with the associatedanvil jaw 41. The cage, which includes the plates 52 and 53, web 54 andpin 56, is carried along with the hammer element 57 `as it revolves. Thedog 57K is guided for rocking movement about the pivot pin 56 due tocamming engagement of the concave inner face 57C of the hammer elementwith the tool head surface adjacent the anvil jaw 41. Upon completion ofthe rocking movement the shoulder 57S on the dog is meshed with theanvil jaw 11. lf the resistance to rotation of the driven bolt, nut, orscrew, is relatively slight, the clutch parts may remain for aconsiderable period of time in meshed relation due to ric tion betweenthe hammer element 57 and the pivot pin 56, and also frictionalengagement between the driving and driven shoulders'57S and 41 on thehammer dog and anvil jaw respectively.

`When the tool head 38 encounters substantial resistl'ance to rotation,the forces holding the clutch in mesh are overcome by the declutchingforce set up by the driving cam 44 against the hammer element 57 and thedog 57R is thereby locked in a releasing direction, which iscounterclockwise, looking forward as in Fig. 3. As soon as the dog 57Ris de-clutched, the motor 23 is relieved of its load and accelerateswith the cage and hammer element to accumulate kinetic energy during onerevolution of the motor, after which the motor, cage and hammer elementare stopped upon delivery of an impact through the shoulders 57S and 41.The rotational impacts are repeated as long as the operator holds thewrench socket 50 in engagement with the torque resisting bolt andcontinues the supply of air to the motor, unless sooner terminated bythe automatic control of the present invention.

Rotary air motor Live air is supplied to the tool from an air hoseconnection 60 on the grip handle 21, through a suitable filter 61, andthence through a throttle valve 62 to a handle passage 63, the throttlevalve being controlled by the usual manipulative lever 64 operatingagainst the holding force of a spring 65. After leaving the handlepassage the air passes around an automatic valve 66 (the purpose ofwhich will be described later) into a valve bushing 67, through a seriesof radial ports 68 in the bushing and thence into an air supply chamber69 formed in the control housing 20. Referring to Figs. 1 and 4, liveair flows from the supply chamber through a longitudinal passage 71 anda port leading to the interior of reverse valve bushing 72. From therethe live air is directed, by means of reverse valve 35, into a housingrecess 73R or 73L, depending on the direction of rotation, which isselected by manipulation of the reverse valve lever 36. From the housingrecess the live pressure fluid passes through a longitudinal bore 74R(or 74L), a radial port 75R (or 75L) and another longitudinal port 76Ky(or 76L) leading to a cylinder recess 77R (or 77L) at 'one end of thecrescent shaped chamber in the motor. 'The rotor 31 turns, in a mannerwell known in the art, )by the action of live air passing through thecrescent :shaped chamber 32 and expanding in the pockets or :spacesbetween the blades 34. The exhaust air flows from the cylinder recess77L (or 77K) through longitudinal bore 76L (or 76R), radial port 75L (or75R), longitudinal bore 74L (or 74K), housing recess 73L (or 73K),through an opening into reverse valve bushing 72 and thence throughexhaust port 79 to atmosphere.

The impact clutch 51, 57, 38, the air motor 23 for driving the clutchand the reverse valve 35, 36 for controlling the direction of rotation,all of which have been described in detail, are conventional structuresby themselves. The present invention relates to the combination of sucha device with the automatic valve 66 which is arranged to cut olf thesupply of live air and therefore stop the rotation of the clutchautomatically upon attainment of a predetermined maximum load on thetool head 38. The novel mechanism for automatically releasing theautomatic valve will now be described.

Automatic cut-O valveV Referring to Figs. l, 6 and 7, the valve 66 issurrounded by a coiled compression spring 81, interposed between thehead 82 of the valve and the bottom of the recess in the valve bushing67, whereby the spring at all times urges the valve outward or towardthe open position. When the throttle valve 62 is closed, as shown inFig. 1, the pressure of the spring 81 is unopposed and acts to seat theouter extremity of the automatic control valve 66 against a plug 83secured to the control housing 20. rlfhe automatic valve 66 has a stem84 slidably tting the bushing 67 and terminating in an inward extensionor projection 85 separated from the main stem by a shoulder 86. In theidle condition of the parts, as shown in Fig. 1, the

projection acts as a stop for a double arm lever or trigger 87 pivotedon a pin 88 supported transversely in the control housing 20. Thetrigger is held in contact with the valve extension 85 by yieldablemeans such as compression spring 89. Upon depression of thethrottlelever 64, the operator admits live air through the handle passage 63 toinitiate operation of the tool as previously described. The uid pressurein passage 63 acts against the outer end of the automatic valve and,being unbalanced over the area of the valve stern 84, overcomes therelatively light spring 81 and shifts the control valve inward until thevalve shoulder 86 seats against the trigger 87 as shown in Fig. 6. Aslong as the trigger remains in the Fig. 6 position it holds the controlvalve 66 open to drive the motor 23.

Control for automatic valve The apparatus for automatically operatingthe trigger 87, to release it from the path of the automatic valve, willnow be described. Referring to Figs. 6, 9 and 10, the rear shaft 29 onthe rotor 31, which projects into the control housing 20, has threelongitudinally extending grooves 91 adapted for the reception of balls92. A cam sleeve 93, shown best in Figs. 14, l5 and 16, is provided withinternal grooves 94 cooperating with the balls to form a splinedconnection allowing limited relative axial (but not rotative) movementbetween shaft 29 and the cam sleeve. The peripheral surface of the camsle-eve is generally cylindrical and tits a counterbore within ailywheel or inertia sleeve 95, shown best in Figs. l1 and 12. In theidle condition of the parts, and also during the first part of theoperation of the tool, the cam sleeve 93 occupies a forward position inthe ily-wheel as shown in Fig. 6.v The cam sleeve drives the ily-wheelthrough a ball cam arrangement adapted to transmit to the ily-wheel arotational component of force and in addition an axial component tendingto shift the ily-wheel forward or the cam sleeve rearward. The ily-wheel95 cannot move forward because its front face seats against the innerrace of ball bearing 27. Therefore the camming action between the camsleeve 93 and the ily-wheel tends to move the cam sleeve rearward towardthe position illustrated in Fig. 7. In order to effect the desiredcamming action the cam sleeve 93 is provided on its outside surface withthree equally spaced grooves or pockets 97, all of the same size andshape, each having sides 97K and 97L, tapering from the front edge ofthe cam sleeve and joined by a rounded vertex. As shown in Fig. 14, eachgroove 97 is rounded in cross section to t a ball 98 along either sideof the groove. The ball is adapted in its normal position to seat in therounded vertex between sides 97R and 97L' and to roll forward along oneof the sides toward the open end of cam groove 97 upon relative movementbetween cam sleeve 93 and the ily-wheel.

Fly-wheel 95 has three tapered grooves or pockets 99 formed in itscounterbore and open at the rear side of the latter. Each groove hassides 99K and 99L joined by a rounded vertex at the front end of thegroove. As shown in Fig. 12 each groove 99 is rounded in cross sectionto t the ball 98 along either side of the groove. The ball is adapted inits normal position (Fig. 6) to seat in the rounded vertex between sides99R and 99L and to roll rearward along side 99R or 99L toward the openend of groove 99 upon relative movement between cam sleeve 93 andfly-wheel 95. The shape and dimensions of groove 99 conform as nearly aspossible with groove 97 and the sides 99R and 99L are spirally inclinedat the same angle, say, an angle of 15 Assuming that the tool is runningin a right hand direction (clockwise, looking forward), the ball 98 isarranged for rolling engagement along the sides 97R and 99K as the camsleeve 93 is displaced relative to the iiy-Wheel from the Fig. 17 to theFig. 18 position and back again. Similar rolling engagement takes placebetween the sides 97L and 99L when the tool is operated to deliverimpacts in a left hand direction, as will be explained more fullyhereinafter.

Yieldable means is provided to constantly urge the cam sleeve forwardand to tend to hold it in the position of Figs. 6 and 17 with the balls93 seated in the vertices of cam grooves 97 and 99. Such means islocated within the control housing which also encloses the cam sleeve93, fly-wheel 95 and trigger 87. The yieldable means comprises a leafspring 101 (Figs. 6, 7 and 8) having a fulcrum portion partly encirclinga transverse pin 102, a short arm extending rearward therefrom, and along arm extending inward from the fulcrum portion. At or near its freeend the long arm is interposed between the inner end of trigger 87 and abutton 103. The buttonis mounted in a ball bearing 104 which in turn issupported in a cam sleeve extension 105 seated in the rear end the camsleeve 93. A set screw 106 threaded in the wall of control housing 20,has an inner end abutting against the short arm of leaf spring 101 nearthe free end thereof. The purpose of the set screw is to provide anadjustable tension on spring 101 which acts through the button 103, ballbearing 104, cam sleeve extension 105, and cam sleeve 93. The set screw106 has a kerf or slot 107 adapted to receive a screw driver by means ofwhich the screw may be adjusted from outside the housing 20.

Assume that the operator desires to tighten a bolt, having right handthreads, to the required degree of tightness as predetermined byadjustment of the set screw 106. He checks, or re-sets, the position ofthe reverse valve 35, moves the entire tool until the wrench socket 50rests on the head of the bolt, depresses the throttle lever 64 andsimply holds the lever down with the tool in position. The action fromthat time on is automatic and independent of the skill of the operator.Live air flows past the throttle valve 62, through handle passage 63,past the automatic control valve 66 (in the Fig. 6 position) into airsupply chamber 69, through passage 71, past reverse valve 35, into motorhousing recess 73K (Fig. 4) and through passages 74R, 75l?` and 76K tocylinder recess 77R. The live air drives the motor 23 in a clockwisedirection (looking forward) by acting against the slidable blades 34 inpassing through the crescent shaped chamber 32. The exhaust air flowsfrom the cylinder recess 77L, through passages 75L, 74L, 73L and pastthe reverse valve to atmospheric exhaust port '79.

As the motor 23 turns, its front rotor shaft 30 carries with it theclutch driving cam 44 (Fig. 3) which imparts clockwise revolution to thehammer assembly including hammer element 57 and supporting cage 51. Thedog 57R on the hammer element engages the anvil jaw 41 to drive the toolhead 38, wrench socket and driven bolt (not shown) all at the same speedas the motor. As the head of the bolt comes into contact with the work,there is a sudden increase in the resistance to rotation of the bolt,wrench socket S0, tool head 3S and anvil jaw 41. The reaction istransmitted back to hammer element 57, hammer cage 51, clutch drivingcam 44 and motor 23, causing the motor to decelerate from a free runningspeed of, say, 3000 R. P. M. to a somewhat lower speed. During thisdeceleration, the impact clutch is released because the hammer element57 is driven with a declutching component of force tending to rock thedog 57K counterclockwise about the pivot pin 56. Following release, themotor is permitted to accelerate during one complete revolution as thehammer element 57 is carried around the anvil jaws 41 and moves throughthe positions shown in Figs. 2 and 5. When the hammer element 57reengages, as in Fig. 3, it delivers an impact over the shoulders 57Sand 41, and the frictional engagement therebetween locks `the hammerelement against declutehing movement until the impact has terminated.During the delivery of the impact the clutch driving cam and the motorare alsoloeked against anymovement relativeto 8 the anvil jaws 41. Upontermination of the impact the clutch driving Vcam 44 rocks the hammerelement 57 out of driving position and the rotating parts accelerate foranother 360 degrees until the hammer dog 57R again strikes the anvil.The rotational impacts are delivered in rapid succession, each blowbeing effective to turn the tool head 38 by a few degrees and thus toincrease the tightness of the driven bolt or threaded fastener, in amanner well known in the art.

Generally speaking, each succeeding blow of a series occurs over ashorter period of time, with a shorter degree of turning movement of theanvil, with a greater force of blow and with a greater amount ofdeceleration of the motor, as the bolt is driven tighter and meets withincreasing resistance. It should be understood, however, that aninstantaneous deceleration of the motor which occurs only during aninfinitesimal period of time is not a reliable indication of thetightness of the driven nut. The reason is that the force of the blow isdelivered in two stages, the first of which is instantaneous andvariable with factors unrelated to the tightness of the bolt, and thesecond stage of which is of finite duration and proportional to theresistance or tightness of the driven element. When the striking face57S of the hammer dog 57K hits the anvil jaw 41, the `first effect is tostart the tool head 38 and wrench socket 50 from rest and acceleratethem to the speed at which they turn the driven bolt. The tool headaccelerating stage occurs only for an infinitesimal time which isfollowed by the werking stage of finite duration in which the tool headdoes the work of turning the bolt against its resistance. As the boltbecomes tighter, the distance traveled during each working stage ofimpact becomes less and the time required to arrest rotation of thehammer assembly 51, 57 is correspondingly shortened with a correspondingincrease in the force of blow and in the deceleration of the hammerassembly. In the case of the first stage of the impact, however, theamount of force required to accelerate the tool head 38 and wrenchsocket 50 is not proportionate to the degree of tightness of the drivenbolt, but depends chiey on the speed of the motor just before impact. Infact, the maximum instantaneous impact force probably occurs on thefirst blow because of the high motor speed, whereas on subsequentimpacts the motor is limited to the speed that it can attain afterstarting from rest and turning only 360 degrees, or perhaps a fewadditional degrees in the case of rebound.

In accordance with the present invention, the torque control device isarranged to be responsive to a predetermined amount of motordeceleration of finite duration, but unresponsive to motor decelerationof the same or even higher value which occurs instantaneously or for aninfinitesimal period of time. Referring to Figs 6, ll, l5 and 17, whenthe motor 23 starts from rest, either upon initial operation of the toolor at the end of one impact in a series, the rear shaft 29 on the rotordrives the inertia sleeve through a connection which includes cam edge971., ball 98 and cam edge 99L. This connection is arranged to resolvethe driving force into two components, one rotational and the other inan axial direction tending to displace the cam 93 rearwardly. During thetime that the motor is increasing its speed the driving force throughthe ball cam connection is not sufficient to overcome the holdingpressure of leaf spring 101 and the ball cam 98 therefore remains in itsnormal or Fig. 17 position up to the time of delivery of an impact. Thecam 93 and fly-wheel 95 rotate in unison in the direction indicated bythe arrows in Fig. l7. When the hammer dog 57R strikes the anvil jaw 4l,the motor 23 stops suddenly or encounters an abrupt reduction in speed.Upon such deceleration of the motor with its rear shaft 29, the ball camarrangement reverses its action and the fly-wheel 95 drives the motorshaft .through the edge 99K, ball 98 and edge 97K. The inclination ofthese sides-or edgestendsto shift the cam 93 rearward. Upon delivery ofthe lirst impact there is a sharp instantaneous deceleration of themotor, as the hammer element 57 accelerates the tool head 38 and wrenchsocket 50. During this brief instant of maximum deceleration the drivingforce of the flywheel 95 rises to a value suicient to dislodge the balls98 from the bottoms of the pockets 99 and 97 and to cause the cam sleeve93 to shift rearward. Before the sleeve has moved substantially, theforce of the blow is attenuated and `during the working portion of therst impact the cam sleeve is restored to the position of Figs. 6 and 17.During subsequent impacts the ball 98 either remains in the Fig. 17position or moves only slightly therefrom, along the edges 99R and 97K.When the bolt is driven to its maximum predetermined degree oftightness, the force of impact and the rate of deceleration of motor 23cause the cam 93 to be moved rearward as above explained.

Torque delivered by the fly-Wheel through the ball cam connection isproportional to the impact torque delivered to the anvil 38 because itis proportionate to the rate of deceleration of the hammer assembly 51,57. The axial component of force on the cam 93 is likewise proportional.Since the deceleration is sustained during the working portion of theimpact, the cam continues to move rearward, against the pressure ofspring 101, until it reaches the position shown in Figs. 7 and 18.During such movement the cam acts against the cam extension 105, ballbearing 104, button 103 and spring 101 to rock the trigger 87 againstthe pressure of spring 89. As soon as the trigger is rocked to the Fig.7 position it frees the shoulder 86 of automatic control valve 66 topermit the valve to move inward. The valve is moved inward by thepressure of live air action over the stem portion 84 of the valve untilthe head 82 seats against the valve bushing 67 to cut olf the supply ofair to the motor 23.

The control valve remains closed and the motor remains at rest as longas the operator holds the throttle level 64 down. In order to conditionthe tool for starting a new cycle of operation, the operator releaseslever 64 to close throttle valve 62. Thereupon the pressure acting oncontrol valve 66 is relieved to permit the light spring 81 to open thevalve with the result that the trigger 87 moves back to its Fig. lposition, seated against the reduced extension 85 on the valve. In orderto overcome delay in restoration of the valve which might be caused bylive air trapped in handle passage 63 the valve 66 is provided with acentral opening 109. When the valve is in its innermost position theopening 109 bleeds air from handle passage 63 into the control housing20 which is vented by any suitable means, such as a hole 110, or apassage into the motor exhaust chamber.

The operator moves the impact wrench from one bolt to another, merelyapplying the wrench socket`50 to the bolt head, depressing the throttlelever 64, waiting until the tightening operation is completed releasingthe lever and pressing again for the next bolt. To establish the desiredadjustment a driven bolt is tested with a hand torque wrench. If greater(or less) tightness is desired, the set screw 106 is turned to increase(or reduce) the pre-load on spring 101.

The forces and design factors of the torque control for the impactwrench illustrated in Figs.' l-l8 are related as follows:

24= T zl LXI F=pre1oad of spring 101 (in pounds) T=delivered torque atcut-olf (foot pounds) =moment of inertia of fly-wheel 95 I=mon1ent ofinertia of hammer assembly 57, 51,

clutch cam 44 and rotor 31 f L=lead of ball cam edges 97R and 99R(inches per revolution) Preferably the combined inertia of the tool heador anvil 38 should not exceed 5 percent of the hammer and rotor assembly57, 51, 44, 31 to provide reasonable torque accuracy and preventpremature cut-off. The amount of displacement of cam 93 required torelease the control valve 66 should be small enough to providereasonabletorque accuracy but large enough to prevent prematurel cut-offdue to inertia of tool head 38. In a physical. embodiment of theinvention which has been tested suc-- cessfully, the cam 93 is displacedabout 40 or 50 thou-v sandths of an inch against a spring force whichmay be: adjusted within the range between l5 and 30 pounds.. The torquedelivered by the tool is adjustable between 300 and 600 foot pounds.Torque variation is less than,I plus or minus l0 percent. The accuracyof the device is due in part to the use of balls which minimizefriction. Torque delivered at any setting of the screw 106 is virtuallyunaffected by live air pressure variations between 50 and 100 pounds persquare inch providing the pressure is high enough to develop therequired torque. In short the performance of the control ydevice is notseriously affected by normal variations in motor performance. Torquedelivered to a 3M inch bolt is the same as that delivered to a one (l)inch bolt. Torque delivered at any setting is virtually unaffected bythe addition of long extension Shanks, universal joints, slip chucks,etc. providing the addition of such accessories does not reduce theultimate torque to a value lower than that to which the control deviceis adjusted. It is alsosubstantially independent of the Work rate. Thatis, a gathering job, in which the bolt approaches its maximum resistance gradually will receive the same nal torque as a sudden stopjob.

The embodiment of invention illustrated in Figs. l-l8 is symmetrical,and upon selected setting of the reverse lever 36 will drive a bolt withleft hand threads to the same degree of tightness as a right hand bolt.

Modified )ty-wheel and cam In a modied form of this invention,illustrated in Figs. 19-24, and diagrammatically in Figs. 28 and 29, thefly-wheel 112 moves axially when cam action occurs. As shown in Figs.24, the fly-wheel has a bore 113 and a counterbore 114 extending forwardtherefrom to the front face of the ily-wheel. An inner cam member 115(Figs. 2l and 22) has a cylindrical portion 116 tting the counterbore114 and a rear extension 117 fitting the bore 113.` The cylindricalsurface of the counterbore is interrupted by three spaced grooves orpockets 118 open at lthe front end. Each groove has sides 118R and 118Ltapering rearwardly and joined by a rounded vertex at the rear end. Eachpocket is rounded in cross section to receive a ball 120. The inner cam115 is provided with three spaced pockets 121 formed on the cylindricalportion 116 and open at the rear end thereof. Each pocket has sides 121Kand 121L tapering forwardly and joined by a rounded vertex at the frontend. The shape, dimensions and functions of the pockets 118 and 121correspond to those of pockets 99 and 97 respectively in the embodimentfirst described, except that they are oppositely directed. That is tosay, the cam drives the fly-wheel, and the balls normally rest in thevertices of the pockets in the case of the Fig. l embodiment, but uponrelative rotary move ment, the fly-wheel 112 rather than the inner cammember 115 is displaced rearward.

In front of the cylindrical portion 116, the inner cam 115 has a iiange122 which seats against the inner raceway of ball bearing 27. The frontface of flange 122 is slightly spaced from the rear extremity of a shaft123 which extends rearward from rotor 31. The rotor shaft has a recessreceiving the front end of cam 115 with a splined connection 125, sothat the cam member rotates in unison with the rotor 31 at all times.

The rear extremity of ily-wheel 112 abuts against the inner race of ballbearing 126 which is mounted within a `1 1 button 127. The rear orclosed side of the button abuts against the spring 101 which provides aforward tension on the button, adjustable by means of set screw 106 aspreviously described.

In the operation of the embodiment of invention shown in Figs. 19-25,the rotor 31 starts from rest and as its front shaft drives the impactclutch, its rear shaft 123 drives the fly-wheel 112, acting through thesplined connection 125, cam 115, and ball cam connection 121L, 120,118L. As the fly-wheel is thus accelerated the inclination of pocketsides 121L and 118L has a tendency to shift the ily-wheel rearward butthis tendency is overcome by the pressure of leaf spring 101.Accordingly, the ily-wheel remains in its normal relation to the drivingcam 115, as shown in Figs. l9and 28, with the balls 12@ seated in thevertices of cam pockets 121 and 11S. When motion (in a right handdirection) of the rotor 31 is arrested bythe delivery of an impact, theiiy-wheel 112 continues under its inertia and drives the rotor shaft 123through the ball cam connection HSR, 120, 121R. At the time of eachimpact the ball rolls along the pocket sides 118K and 121R, increasingits degree of movement as blows of increased force are delivered to thehead 38. The balls roll back to the normal position (Figs. 19 and 28)after each impact. Upon delivery o-f a sustained blow, of nite durationand of predetermined magnitude, the balls 120 and y-wheel 112 aredisplaced to the position shown in Figs. 20 and 29. The ily-wheel movesbutton 127, which acts through spring 101 to press the trigger 87 torelease position. At this stage the control valve 66 is released forclosing movemen-t as indicated in Fig. 20.

In the form of invention shown in Figs. 19-24 the rotor 31 is relievedof end thrust which otherwise might cause it to rub against the forwardend plate 25.

Modified cam grooves Fig. shows, in development, one of the cam pockets118 in the y-wheel 112. The sides 121L and 121K are symmetrical. That isto say the angle of inclination L of the former is equal to the angle ofinclination R of the latter. As a result the control arrangement ofFigs. 19-25 will operate the same for both directions of rotation andwill release at the same degree of tightness whether the wrench isdriving a right hand or a left hand bolt. It is sometimes desired torelease at a different degree of tightness for diterent directionswithout requiring the re-adjustment of set screw 106. Fig. 26 shows apocket 118 unsymmetrically shaped in order to accomplish that end. Inthis modification the angle L is less than the angle R. The result isthat upon delivery of rotational impacts in a left hand direction theballs 120 transmit a force which has a lesser component in an axialdirection that would be the case if the angle L were equal to the angleR. Therefore the wrench continues to operate on a left hand bolt untilit is driven tighter than would be the case with a bolt having righthand threads. Also, by making the side 121K steeper than the side 121Lit is possible to remove a conventional right hand bolt that has beentightened without changing the setting of screw 106 even though the bolthas been somewhat frozen.

ln Fig. 27 the angle L is reduced to zero which means that the ball camconnection transmits only rotary force, with no axial component, to thefly-wheel 112 upon delivery of left hand or counter-clockwise impacts. Aseries of pockets so shaped may be used to provide an automatic controlfor tightening the bolts and a manual control for loosening the samebolts.

lf the fly-wheel pockets 118 are modified as shown in Fig. 26 or 27,corresponding changes should be made in the angles of the cam pockets121. It willbe understood further that the variations in the pocketshapes as shown in Figs. 26 and 27 are equally applicableto thefly-wheel -12 pockets 99 and cam pockets 97 in the form of inventionshown in Figs. 1-18.

While the invention has been described with reference to a clutch of thetype which is driven directly by the motor, it is also applicable toimpact wrenches of the accumulator type in which the motor runscontinuously. In adapting the present invention to an accumulator typeimpact wrench, the ball cam drive for the y-Wheel would be operated notby the motor but by a spindle or other element that starts and stopsalong with the hammer assembly. in the case of an electric wrench thecontrol device of the present invention may be arranged to open a switchinstead of closing a valve.

If desired, the screw 106 may be provided with a calibrated torquesetting dial. This would be useful in yautomotive repair shops where itis desired to adapt the tool quickly for driving different kinds of nutshaving known torque requirements.

What is claimed is:

l. An impact wrench comprising a rotatable anvil, a rotatable hammerassembly arranged to drive said anvil and to deliver a series ofrotational impacts thereto, a rotatable motor having a rotor for drivingthe hammer assembly, a rotating shaft connected with the hammer assemblyand arranged to start and stop in substantial unison with the hammerassembly and rotor whereby the combinedv kinetic energy of the rotor,hammer assembly and shaft is delivered to the anvil upon impact, andmeans responsive to a predetermined deceleration of the shaft prior tothe stopping thereof for cutting off the supply of power to the motor.

2. An impact wrench comprising a tool head adapted to drive a threadedfastener, a rotatable hammer arranged to deliver a series of rotationalimpacts to the tool head, a rotating shaft connected to the hammer andarranged to decelerate together with the hammer, a trigger device,inertia means for operating the trigger device in response to apredetermined deceleration of the rotating shaft, means forautomatically terminating rotation of the hammer upon operation of thetrigger device, and means for delaying operation of the trigger device,to prevent operation of the terminating means in response to hammerdeceleration of extremely `short duration upon acceleration of the toolhead during delivery of the first impact of a series.

3. An impact wrench according to claim 2 in which the inertia meanscomprises an inertia sleeve and a driving connection between therotating shaft and the inertia sleeve.

4. An impact wrench according to claim 3 in which the driving connectionbetween the rotating shaft and the inertia sleeve comprises mutuallycooperating cam elements carired by the shaft and inertia sleeverespectively, said cam elements having relative axial movement upondevelopment of relative rotative movement between the shaft and inertiasleeve.

5. An impact wrench according to claim 4 in which the trigger isoperated in response to such relative axial movement.

6. An impact wrench comprising a rotatable anvil, a rotatable hammerelement arranged to drive said anvil and deliver a series of rotationalimpacts thereto, a rotary air motor having a rotor for driving saidhammer ele' ment, said rotor and hammer element being arranged to startand stop in substantial unison, a valve for supplying live air to themotor for driving the same, and means for automatically closing thevalve to stop the motor upon development of a predetermined decelerationof the hammer element, said means being operable during the delivery ofan impact but being ineffective upon delivery of an impact of shortduration occurring as the first impact of a series.

7. An impact wrench comprising a rotatable anvil, a rotatable hammerarranged to drive said anvil and to dev liver a series of rotationalimpacts thereto, a rotary air motor for driving said hammer, a rotatingshaft connected with the hammer and arranged to decelerate along withthe hammer upon delivery of a rotational impact, a valve for supplyinglive air to the motor for driving the same, and inertia means forautomatically closing the valve to stop the motor upon development of apredetermined deceleration of the rotating shaft, said inertia meanscomprising a ily-wheel, and a driving cam interposed between the shaftand fly-wheel to drive the latter, said ily-wheel being rotatablerelative to the shaft upon deceleration thereof, and said driving cambeing axially movable relative to the shaft and fly-wheel upon rotationof the fly-wheel relative to the shaft.

8. An impact wrench comprising a rotatable anvil, a rotatable hammerarranged to drive said anvil and deliver a series of rotational impactsthereto, means for driving the hammer, means including a trigger forstopping the rotation of the means for driving the hammer, automaticinertia means responsive to a predetermined deceleration of the hammerfor operating the trigger, and means for delaying operation of theautomatic means to prevent actuation of the trigger in response todeceleration of extremely short duration.

9. An impact tool comprising an anvil, a rotatable hammer arranged todeliver a series of impacts to said anvil, a rotatable shaft connectedto the hammer and having intermittent rotary movement in substantialunison with the hammer, a rotatable driving means for the hammer, afly-wheel driven by the shaft through a flexible connection, saidily-wheel being movable at times in unison with the shaft but beingcapable of rotating ahead of the shaft upon sudden deceleration of thelatter, automatic means responsive to relative movement between thefly-wheel and shaft for discontinuing rotation of the means for drivingthe hammer, and means for inhibiting operation of said automatic meansin response to an impact of short dura-tion occurring as the firstimpact of a series.

10. An impact tool according to claim 9, in which the exible connectioncomprises one or more pairs of cooperating inclined grooves, one groovecarried by the shaft and the other by the ily-wheel, said grooves beingarranged to cause relative axial movement between the fly-wheel andshaft upon relative rotative movement therebetween.

11. An impact tool according to claim 10 in which a spring is arrangedto resist such axial movement.

l2. An impact tool according to claim 11 in which manipulative means isprovided to adjust the tension of the spring and hence the rate ofdeceleration of the shaft required to discontinue rotation of the meansfor driving the hammer.

13. An impact tool according to claim 11 in which one 0r more balls areinserted between the cooperating grooves to minimize friction.

14. An impact tool according to claim 13 in which the groove carried bythe shaft is in the form of a V-shaped pocket, the sides of whichfunction in different directions, the inertia member being provided witha complementary V-shaped pocket.

15. An impact tool according to claim 14 in which the sides of thepocket are symmetrical whereby the means for discontinuing the drivingof the hammer responds to fthe same deceleration thereof in eitherdirection of rotation.

16. An impact tool according to claim 14 in which the sides of thepocket are asymmetrical whereby the means for discontinuing the drivingof the hammer responds to a different deceleration of the hammer whendriven in one direction than when driven in the other direction.

17. An impact tool according to claim 14 in which one side of the pocketis inclined and the other parallel to the axis of rotation whereby themeans for discontinuing rotation of the hammer is elfective only for onedirection of rotation.

References Cited in the file of this patent UNITED STATES PATENTS2,261,204 Amtsberg Nov. 4, 1941 2,326,347 Forss Aug. 10, 1943 2,425,793Fosnot Aug. 19, 1947 2,543,979 Maurer Mar. 6, 1951 FOREIGN PATENTS v1,050,484 France Sept. 2, 1953

